This invention relates generally to the field of fluid drop generation and the application thereof to jet drop recorders of the type shown in U.S. Pat. No. 3,701,998 to Mathis, issued Oct. 31, 1972. In recorders of this type, a pair of rows of orifices receive an electrically conductive recording fluid, such as for instance a water base ink, from a pressurized fluid manifold and eject the fluid in two rows of parallel streams. The fluid flows through orifices in a plate with the formation of drops being stimulated by the application of a series of traversing waves to the plate. This method of drop generation is more completely described in U.S. Pat. No. 3,739,393 to Lyon et al., issued June 12, 1973.
Graphic reproduction in recorders of this type is accomplished by selectively charging and deflecting some of the drops in each of the streams and thereafter depositing the uncharged drops on a moving web of paper or other material. The direction of web movement is substantially perpendicular to the rows of orifices. Charging of the drops is accomplished by application of charge control signals to charging electrodes near the edge of the streams. As the drops separate from their parent fluid filaments, they carry a portion of the charge applied by the charging electrodes. Thereafter, the drops pass through electrostatic fields which have no effect upon the uncharged drops but which cause the charged drops to be deflected. Drops which are not to be printed are charged sufficiently to be deflected to one or the other of a pair of catchers which service the rows of streams.
U.S. Pat. No. 3,787,883 to Cassill, issued Jan. 22, 1974, discloses apparatus for creating the deflecting electrostatic fields. A thin deflection ribbon is positioned between and parallel to the two rows of parallel drop streams with the catchers positioned outwardly of the drop streams. A voltage is applied between the deflection ribbon and the catchers such that charged ink drops will be deflected to one of the two catchers.
One problem with printers of this type and with all types of ink jet printers has been attaining sufficient image resolution. Since a discrete number of drops are applied to form the images, it is clear that image definition may be improved by increasing the number of drops and providing a proportionate increase in data handling capability. If, however, only one print position per print line is serviced by each orifice, the number of drops per unit width and therefore the resolution of an image in the direction transverse to the web is limited by the minimum dimensions required for each orifice. The approach taken in the Mathis device is to provide two rows of drop streams which are staggered. The charging of drops in the two rows is timed such that printing from the two rows of streams is in registration. The distance between adjacent streams in each of the rows is therefore twice the distance which would separate streams in a printer of comparable resolution having one row of streams.
Another approach to this problem is shown in U.S. Pat. No. 3,373,437, issued to Sweet et al. on Mar. 12, 1968, and assigned to the assignee of the present invention. FIG. 6 of the reference shows a configuration in which the jets in a single row are formed in a converging array, thus permitting greater spacing between the individual orifices and their accompanying charging electrodes. Such a configuration is, however, disadvantageous in that the distance traveled by the drops in each stream will be slightly different, and as a result, data timing will be very complicated. Additionally, it is somewhat difficult to insure that the streams continue to converge as they approach the web.
In U.S. Pat. No. Re. 28,219, issued Oct. 29, 1974 to Taylor et al., and assigned to the assignee of the present invention, a printer has a plurality of separate orifice arrays positioned in tandom, with each successive array being laterally offset. The orifices are positioned such that they interlace to provide print capability across the entire web. The orifice arrays, like the two rows of orifices in the Mathis printer, extend perpendicular to the direction of web movement. The Taylor et al printer, like those of Sweet et al and Mathis, is binary, i.e. a drop formed at an orifice is either printed at one predetermined position on the moving web, or it is deflected to a catcher and not printed at that predetermined position.
Another approach is shown in U.S. Pat. No. 3,739,395 to King, issued June 12, 1973 and assigned to the assignee of the present invention. In the King device, uncharged drops are caught and thus do not print while charged drops from each orifice are deflected by two sets of deflection electrodes to a plurality of discrete print positions on the moving web. Deflection of the drops is either perpendicular or parallel to the direction of web movement, or both, covering either a one line matrix or a multiple line matrix on the web. Since a number of print positions on the web are serviced by a single jet, the distance between orifices may be greater than if each orifice serviced only one print position. The minimum distance between orifices is somewhat greater with the King device, however, since deflection electrodes must be positioned on all sides of each orifice.
U.S. Pat. No. 3,871,004, issued Mar. 11, 1975 to Rittberg, discloses a writing head which moves transversely with respect to a print web. Individual deflection electrodes are arranged adjacent each orifice on the print head such that drops may be deflected obliquely to the direction of head movement to one of three print positions. The orifices are positioned in a row perpendicular to the direction of head movement. The Rittberg device requires separate deflection electrodes for each individual jet. Additionally the electrode configuration is somewhat bulky, thus further limiting the minimum inter-orifice spacing.
The concept of increasing image resolution by increasing the number of print positions serviced by a single ink jet is also shown in U.S. Pat. No. 3,813,676, issued May 28, 1974 to Wolfe; U.S. Pat. No. 3,769,631, issued Oct. 30, 1973 to Hill et al.; and U.S. Pat. No. 3,298,030, issued Jan. 10, 1967 to Lewis et al. These patents show printing arrangements in which a single jet prints an entire line of characters as the print web is moved past the jet. The Wolfe reference shows deflection of the jet oblique to the direction of web motion to increase symbol printing flexibility.
Thus while various approaches have been taken to increase the image resolution of jet printers, a need exists for a simple printer capable of high speed printing of a large number of ink drops thus providing increased image definition.